#!/usr/bin/env python

class lindict (dict):
   def __init__ (self, **kwargs):
      dict.__init__ (self, **kwargs)
      self.default = 0.0

   def __getitem__ (self, key):
      try:
         return dict.__getitem__ (self, key)
      except KeyError:
         less = [x for x in self.keys() if x < key]
         more = [x for x in self.keys() if x > key]
         if less and more:
            less = max (less)
            more = min (more)
            key = float (key - less) / (more - less)
            return (1 - key) * self[less] + key * self[more]
         else:
            return self.default

if __name__=='__main__':
   ld = lindict ()

   ld[5] = 20
   ld[10] = 5
   ld[15] = 10

   for i in range (0, 20):
      print ld[i]